This Master Agreement proposal is designed to establish and identify the most proficent chemopreventive agent and conditions that will inhibit, reverse or delay cancer. The work under this master agreement proposal is carried out in coordination with the NCI, in the Division of Cancer Prevention (DCP), using state of the art , mechanism-based models, such that insight may be gained about cancer prevention and control in man. The proposal will provide screening and identification of potential cancer preventive agents in mechanism-based in vitro and in vivo.